The steel cord with an oval cross-section comprising a core and an outer layer has an advantage on stiffness than the steel cord with the round cross-section. There will be different stiffness in the different direction of the oval steel cord, and this character will lead to a good handling, riding comfort or driving stability when such oval steel cord is used for reinforcing rubber tyre. In a direction perpendicular to the long axis of the oval steel cord, there is a decreased stiffness and an increased flexibility so that any obstacles such as cobble stones on the road can be taken easily. In the direction of the long axis of the oval steel cord, there is an increased stiffness and a decreased flexibility leading to an improved stability when taking a bend. Additionally the rubber ply reinforced by the steel cord with an oval cross-section will be thinner than that reinforced by the steel cord with a round cross-section.
Usually, to get such a steel cord with an oval cross-section, the flat wire is used as the core in the steel cord.
EP 0264145 discloses a steel cord with an elongation cross-section comprising a flat wire as the core. The flat wire has a ratio of breadth and the thickness of at least 2. It is a drawback that the flat wire will have a mechanical property loss, e.g. loss of fatigue resistance and less tensile strength, during the manufacturing. The way of manufacturing the flat wire is by means of cold drawing the round wire through a forming profile die or by means of cold rolling. Then the cross-section of the steel wire will be changed from round to flat. Due to the stress-concentration on the four angles of the flat wire, the mechanical properties of the steel wire will loose a lot during the forming process from round to flat. The weak fatigue resistance of the final flat steel wire will take a disadvantage to the final steel cord.
Another way for producing a steel cord with oval cross-section is that arranging the round steel wires based on the geometrical characters of oval, e.g. JP-A-09-268485. The drawbacks are that the ply reinforced by such steel cord is still very thick, the process of manufacturing the steel cord is not very easy to operate, and the producing cost is very high.
WO 93/01375 discloses a steel rope used for reinforcing concrete constructions. The steel rope has an oval cross-section with an oval wire as core. Due to the high elongation of the steel rope and the requirement of the stiffness for reinforcing concrete, the diameter of the steel wire in the rope should be large, larger than 1 mm or even larger than 10 mm. And the carbon content of the steel wire is low, even lower than 0.2%. And steel wires are not provided with a metallic coating such as brass. The patent application document discloses that a steel rope with such structure can be used for reinforcing concrete construction. Due to low carbon content and big diameter, the steel rope does not adapt for reinforcing rubber product.